PROJECT SUMMARY/ABSTRACT Cardiovascular disease is a major health problem in the western world and in the United States alone accounts for an estimated 500,000 deaths each year. The underlying mechanisms behind sudden cardiac death remain poorly understood. Many types of cardiovascular disorders including ischemic heart disease and heart failure are associated with extensive fibrosis. A critical event in the development of cardiac fibrosis is the transformation of fibroblasts into an active phenotype or myofibroblast. The question of whether fibroblast activation results in a different electrical phenotype that makes the heart susceptible to arrhythmic events remains to be explored. In this proposal, we will investigate the electrical phenotype of fibroblasts isolated from infarcted tissue. We will also work toward identifying new therapeutic approaches designed to alter the electrical phenotype of these cells. The overall aims of the grant are directed at determining whether preventing, delaying or limiting the activation of cardiac fibroblasts has potential beneficial antiarrhythmic effects. We have proposed three specific aims: Specific Aim 1 is to determine the potential of fibroblasts isolated from infarcted hearts to influence impulse propagation and arrhythmogenesis in heterocellular cultures of myocytes and adult fibroblasts. We hypothesize that cardiac injury alters the electrical phenotype of fibroblasts as assessed by high resolution optical mapping of heterocellular cultures. Specific Aim 2 is to determine the electrophysiological mechanisms of fibroblast activation. Here we hypothesize that the electrophysiological phenotype of fibroblasts isolated from infarcted tissue results from the combined effect of an increase in the level of intercellular coupling and a change in the resting membrane potential. Specific Aim 3 is to determine whether one of the pleiotropic effects of the HMG-CoA reductase inhibitors includes improving the conduction properties of infarcted tissue and rescuing the electrical phenotype of fibroblasts isolated from infarcted hearts. In this aim, we hypothesize that the anti-fibrotic properties of statins will attenuate the electrophysiological effects of fibroblast activation as assessed in isolated infarcted hearts and heterocellular cultures of myocytes and fibroblasts. To achieve these aims, we will utilize a combination of molecular biological and cellular electrophysiological techniques, as well as high resolution optical mapping technology at the organ and cellular levels.